1. Field of the Invention
The present invention relates to elevator systems having a plurality of elevator cars that operate in a plurality of elevator shafts and that serve a plurality of elevator landings. In particular, the present invention provides a method and apparatus for assigning new hall calls to one of the elevator cars in the elevator system.
2. Description of the Related Art
Existing hall call allocation systems and methods use criteria, such as waiting time, time to destination, energy consumption, and elevator usage, with neural networks, generic algorithms, and/or fuzzy logic to find an optimum solution for assigning a new hall call to one of a group of available elevator cars. These existing systems and methods generally fall into one of two categories; Estimated Time of Arrival (xe2x80x9cETAxe2x80x9d) based systems and destination dispatch based systems.
The prior art systems and methods have certain inherent shortcomings that limit their efficiencies. ETA based systems calculate the amount of time required for each available elevator to answer a new hall call. The elevator with the lowest time required to answer the call, i.e., the car that will arrive first, is assigned the new hall call. While ETA based systems have some advantages, they do not adequately evaluate the negative impact of a new hall call assignment on existing call assignments. For example, when a passenger enters a new hall call and it is accepted by an elevator car carrying existing passengers that are traveling to a floor beyond the floor where the newly assigned hall call was entered, the existing passengers will be delayed by the time needed to pick up the new passenger and, depending upon the new passenger""s desired destination, the existing passengers may be delayed by the time needed to drop off the new passenger.
Destination dispatch systems also have shortcomings. For example, they require a destination input device at each elevator landing and usually have no call input devices in the elevator car. Because destination dispatch systems require entry devices at every elevator landing, they must make an instant call assignment and inform a waiting passenger which car to enter. This instant assignment does not permit an improved assignment if conditions change during the time period between call entry and car arrival. Thus, an elevator hall call assignment system and method that does not require destination entry devices at every elevator landing and that takes into account the delay that a new hall call assignment will have on existing passengers would greatly improve the elevator art.
An elevator system having a plurality of elevator cars that are capable of making stops at a plurality of elevator landings may use a computer implemented method to assign a new hall call to one of the elevator cars. In some situations, the elevator cars may have previously been assigned car calls and hall calls, i.e. they have may have existing car calls and existing hall calls. The method comprises receiving a new hall call signal from an elevator landing where a passenger is requesting an elevator car and, for each elevator car, calculating a call cost for accepting the new hall call. The call cost for each elevator car is calculated by inferring a destination for the passenger(s) entering the new hall call. Destinations may be inferred from statistical data or other means that are known in the art. After the destination is inferred, an estimated time to the inferred destination (xe2x80x9cETIDxe2x80x9d) is calculated for each car. For each car, system degradation factors (xe2x80x9cSDFsxe2x80x9d) are calculating for any and all existing hall calls and car calls. A system degradation factor for an existing car call is a function of the delay that one or more passengers traveling on the elevator car will experience as a result of the car""s acceptance of the new hall call. A system degradation factor for an existing hall call is a function of the delay that the passenger(s) who requested the existing hall call will experience as a result of the elevator car""s acceptance of the new hall call.
Once the estimated time to the inferred destination is calculated and the system degradation factors are calculated, the call cost value (xe2x80x9cCCxe2x80x9d) for an elevator car can be calculated according to the following equation:   CC  =                    ∑                  k          =          1                n            ⁢              SDF        k              +    ETID  
wherein the elevator car has a quantity of n existing car and hall calls(k). The new hall call is then assigned to the elevator car having the lowest call cost value.
In elevator systems that employ destination entry devices on some of the elevator landings, or other systems where some passengers"" destinations are known at the time they enter new hall calls, the above method may be modified to achieve better efficiencies. The modified method may be used in elevator systems where some new hall calls contain destination information indicating a passenger""s specific desired destination and some do not contain destination information indicating a passenger""s specific desired destination. For new hall calls containing destination information, an estimated time to the actual destination (xe2x80x9cETDxe2x80x9d) is calculated for each elevator car. For new hall calls not containing destination information, a destination is inferred for the new hall call and an estimated time to the inferred destination is calculated for each elevator car in the system. Also, for each car, system degradation factors for existing hall calls and existing car calls are calculated. Finally, a call cost value for accepting each new hall call is calculated as follows:
for new hall calls accompanied by destination information the CC is calculated as follows:   CC  =                    ∑                  k          =          1                n            ⁢              SDF        k              +    ETD  
wherein each car has a quantity of n existing car and hall calls(k); and
for new hall calls not accompanied by destination information the CC is calculated as follows:   CC  =                    ∑                  k          =          1                n            ⁢              SDF        k              +    ETID  
wherein each car has a quantity of n existing car and hall calls (k). The elevator cars having the lowest call cost is assigned to the new hall call.
The improved assignment method described above is preferably implemented in an elevator system having a plurality of elevator landings and a plurality of elevator cars that are available to answer new hall calls. The system may have internal elevator car destination entry devices for allowing passengers to enter desired destinations after they enter an elevator car. The system may also have, on some landings, external elevator car destination entry devices for allowing passengers who are requesting a new hall call to enter a desired destination. A computer touch screen is particularly well suited for use as an external elevator car destination entry device. On other elevator landings, the system may contain standard up/down hall call entry devices that allow passengers to hail elevator cars. The elevator system employs an elevator controller that is electronically interfaced with these devices and is programmed to receive signals from these devices and calculate, for each available elevator cars, call costs for accepting one or more of the new hall calls. The elevator controller is further programmed to assign new hall calls to the elevator cars having the lowest call costs. The controller may be configured to recalculate call cost and re-assign new hall calls as passengers enter or exit elevator cars and/or as passengers enter new car calls. The elevator controller may also be interfaced with elevator load sensors on each elevator car so that each elevator car""s load can be calculated and used to approximate the number of passengers in the elevator car. This approximation can be used to improve call cost calculations.